Abstract The proposed study focuses on improving sun protection and skin surveillance practices among young onset melanoma survivors and their first degree relatives (FDRs). As a group, young onset survivors have been identified by the National Cancer Institute as a unique and growing population. Survivors are at higher relative risk for a second malignancy than adults diagnosed with cancer over 39 years of age. FDRs of young melanoma patients are at increased risk for melanoma. Melanoma survivors and their FDRs should engage in regular total cutaneous exams, comprehensive skin self-examinations, and sun protection. Despite their increased risk and the fact that this population is growing, FDRs pay relatively little attention to sun protection and skin surveillance behaviors. Although the vast majority of young onset melanoma survivors engage in regular total cutaneous exams, many do not engage in regular skin self-exams or sun protection. There is no intervention research targeting the unique and growing population of young onset survivors and their FDRs. The proposed study expands an effective behavioral intervention to improve total cutaneous exams, skin self- exams, and sun protection behaviors among FDRs of survivors of all ages to young onset patients and their FDRs. We will deliver the intervention via secret groups on Facebook comprised of FDRs and young onset patients from multiple families. Our pilot work demonstrates we can engage families in a Facebook group. We will randomize 577 FDRs and 583 young onset survivors to one of two study arms: a 12-week Young Melanoma Family Facebook intervention or a 12-week Healthy Lifestyle Facebook intervention. Participants will complete a baseline, post-intervention, and a 6-month post-intervention survey. The study has one primary and two secondary aims. The primary aim (FDRs) is to examine the efficacy of the Young Melanoma Family Facebook intervention versus the Healthy Lifestyle Facebook intervention on total cutaneous exam (primary outcome), skin self-exam frequency and comprehensiveness, and sun protection practices (secondary outcomes) of FDRs of young melanoma survivors. A secondary aim (survivors) is to examine the efficacy of the Young Melanoma Family Facebook intervention on patients' skin self-exam frequency and comprehensiveness and sun protection habits. Another secondary aim is to examine the mechanisms of intervention efficacy.